Dómine, ad adiuvándum meum festína.
We use an imperative, from festinare: festina = Hurry / rush / make haste.
We call him Domine, from Dominus = Lord. This is the vocative case because we are addressing Him: “O Lord.” The second declension (ending in –us) has a specific form for the vocative case = us becomes e. The vocative exists in all other declensions but its form is identical to the nominative form.
How would you say ‘The Lord will come to help me?’ = Dominus festinabit ad adiuvandum meum.
How would you say ‘O Lord, make haste to help us?’ = Domine, ad adiuvandum nostrum festina.